Professor Paul Bloom: Sex is really strange. You ask people, "What's your favorite activity?" and if you ask people, particularly college students, particularly just fresh from spring break – I've seen teen movies – they'll often answer, "Sex." or some word that is synonymous with sex. But there's a kind of a puzzle about how much time we spend on sex. And it turns out there is data on this. So, people say sex is their favorite activity, but it turns out we actually know how much time the average American spends on sex. And the data I'm going to follow from was summarized in this wonderful book by James Gleick:心理学空间!x S{n{VlF7K`To{
Americans tell pollsters their single favorite activity is sex. In terms of enjoyability, they rank sex ahead of sports, fishing, bar-hopping, hugging and kissing, talking with the family, eating, watching television, going on trips, planning trips, gardening, bathing, shopping, dressing, housework, dishwashing, laundry, visiting the dentist, and getting the car repaired. On the other hand, these same studies suggested the average time per day devoted to sex is four minutes and three seconds. [As Gleick says,] This is not much, even if the four minutes excludes time spent flirting, dancing, ogling, cruising the boulevard, toning up in gyms, toning up in beauty parlors, rehearsing pick up lines, showering, thinking about sex, reading about sex, doodling pornographically, looking at erotic magazines, renting videos, dreaming of sex, looking at fashion magazines, cleaning up after sex, coping with the consequences of sex, building towers or otherwise repressing, transferring, and sublimating .
Qy.K)U(kdxR2tG0And I like this passage because it illustrates two points, two important points. One is we don't actually spend that much time on sex. In fact, the four minutes and three seconds is an interesting number because when you do times studies on how much Americans spend filling out tax-related forms for the IRS, it's four minutes and a few seconds. But the passage also points out that regardless of the brute time we spend on it, it is extraordinarily important. Everything in life follows from it – marriage, family, children, much of aggression, much of competition, much of art and music and creative pursuits. Much of everything follows from it. If we were a creature without sex, everything would be different.
And what's interesting is, there are creatures without sex. There are creatures that reproduce by cloning. And in fact, this basic fact about people – that we fall, roughly, into males and females – is an evolutionary mystery. It's not clear why animals that are somewhat large have two sexes. From a biological Darwinian perspective, having two sexes is bizarre because each time you have an offspring you toss away half your genes. My children only have--each of them have half my DNA. If I were to clone, they would have all of it. And so, it's a puzzle how sex ever evolved.心理学空间z|(y)^3O0zE|$f
This is not a course in evolutionary biology, and that's not the puzzle we're going to be looking at today. We're going to look at a few questions. First, we're going to talk from first a theoretical point of view and then an empirical point of view about how males and females are different. Then we're going to talk about sexual attractiveness, some research about what people find to be sexually attractive, and then we'll talk a very little bit at the end about the origins of sexual preference: why some people are straight, others gay, others bisexual, and others harder to classify.
Now, of all the topics I'm presenting, sex is one of the sort of dicey ones from an emotional point of view. These are difficult issues because sex is, by definition, an intimate part of our lives, and it matters a lot. Moreover, sex is fraught with moral implications. And since I'm talking about this from, at least at the beginning, from a Darwinian evolutionary perspective, I'm obliged to start off by dealing with some of the moral consequences and moral implications.心理学空间'S&tk gF6Dc
8DSY+C)x0So, for instance, many biologists – all biologists I would say – will have argued that sexual behavior, sexual action, sexual desire is, to some extent, a biological adaptation existing to spread our genes. From that perspective then, non-procreative sex – including gay sex, sex with birth control, sex by post-menopausal women – does not serve this reproductive goal and, in some sense perhaps, is unnatural. And one might argue then, "Does this mean it's wrong?" We'll also be talking about sex differences, differences between men and women, for instance, in how much you want anonymous sexual encounters, differences between men and women in social intelligence, in aggression and empathy. And regardless of what you think about these differences, whether you think they're right or wrong or it doesn't matter, you'll ask the question, "To what extent are they mutable?" That is, if they exist through Darwinian natural selection, to what extent can we ever get rid of them? And I want to address those two issues, the issues of morality and inevitability, from the very start. And I want to start off with--for each of them have a quote by a prominent evolutionary scholar. So, the first one is by Steve Pinker inHow the Mind Works. And he writes,心理学空间rMH^VI
Nature does not dictate what we should accept or how we should live our lives. Well into my procreating years, I am so far voluntarily childless, having squandered my biological resources reading and writing, doing research, helping friends and students, and jogging in circles--ignoring the solemn imperative to spread my genes. By Darwinian standards, I am a horrible mistake, a pathetic loser, but I am happy to be that way, and if my genes don't like it they can go jump in the lake.
0V Tq)jR+Fg0Pinker's point, I think, is a reasonable one. It is true that certain things we do exist to serve the dictates of natural selection, but that doesn't make them right? If you think that something is only right if it leads to the generation of more genes, if it leads to reproduction, then you're not going to think very much about birth control. You're not going to think very much about any sort of non-procreative sex. On the other hand, if you're--Moreover, if you think something's wrong if it's unnatural, you're going to think much about flying in a plane or refrigerating food or surviving a severe infection. More generally, our bodies and brains have evolved for reproductive success, but we can use these brains to choose our own destinies. Nothing moral necessarily follows from the facts of biology. That's all I'm going to say about morality. But I want you to keep it in mind when we discuss different claims about what's evolved and what hasn't.心理学空间Z(~IB3aX#w
aN5w+g(R1d1w0What about inevitability? Here I want to turn to Richard Dawkins. Richard Dawkins writes,心理学空间 sy \3[m*s?3m,|;DL
If a child has had bad teaching in mathematics, it is accepted that a resulting deficiency can be remedied by extra-good teaching in the following year. But any suggestion that the child's deficiency might have a genetic origin is likely to be greeted with something approaching despair. If it's in the genes, it is determined and nothing can be done about it. This is pernicious nonsense on an almost astrological scale. Genetic causes and environmental causes are in principle no different from each other. Some may be harder to reverse, others may be easy. What did genes do to deserve their sinister, juggernaut-like reputation? Why are genes thought to be so much more fixed and inescapable in their effects than television, nuns or books.
I like the nuns. And the point here is what causes something is logically separate from what can reverse it. And you can think of clear cases where something is plainly genetic but is fairly easily reversed and where something is cultural and is very difficult to reverse. Here's an example. My eyesight is quite poor. The reason why my eyesight is quite poor is not due to the patriarchy, television, culture or "the man." Rather, my eyesight is quite poor due to the crappy genes Mom and Dad gave me. It is genetically determined if anything is. It is also fairly easy to fix. There are these machines where they put panes of glass in front of your eyes and help you to see better. More advanced machines known as contact lenses actually stick the thing into your eyes, and at the cost of occasional infections you come to see better. It's biologically caused but fairly easy to fix.
On the other hand, take an example of society's treatment of the obese. It turns out when we – and we'll get to this a little bit when we talk about sexual attractiveness – how thin somebody is or how fat they are; what you think of that is actually not particularly hard-wired. It varies a lot from culture to culture. But once it's in a culture, it is almost impossible to shake. So, the point, there is just that genetic does not mean inevitable, and cultural does not mean easy to fix.
Okay. That's general background. Let's start with basic Sex Ed. What's the difference between males and females? Well, don't even think penis and vagina. There are a lot of animals that have neither one. And the difference actually runs deeper. By definition, when biologists talk about this, animals that are males have a little sex cell, which carries genes and nothing else – sperm cells. Animals that are females have a big sex cell, which has genes but also food and a protective cover and all sorts of other stuff. Typically, the little sex cell is much littler than the big sex cell. This is the only erotic picture I'm going to show you today. It's a bunch of these little sperm circling around the egg. It's romantic.心理学空间}~*j#Sp1T"Fl
Q~ ^;]7_N Q%gj0But this raises a puzzle. I just described male and female roughly in terms of a size difference. Males are the smaller of the sex cells; females are the bigger. Why is it then that for so many animals males are the bigger ones, physically, and the more aggressive ones. This has been a puzzle that has occupied scientists for a long, long time. And we're pretty--there is now a pretty clear answer to it. And the answer goes like this. It is based on an idea by Robert Trivers called "parental investment." And what parental investment is, it's defined here as, any investment that's going to increase the offspring's chance of survival at the cost of the parent's ability to invest in other offspring.心理学空间y\%V6`m2ZT _
So, for example, suppose an animal could create an offspring by blinking an eye and then the offspring would run off? That would be extremely little investment. Suppose another animal had to work for ten years, and during those ten years could not create another offspring. That would be a huge investment. Trivers points out that within a species, females typically have a much higher parental investment than males. Because females have these big sex cells, they typically incubate them internally. They carry them. If they're eggs, they might have to sit on them. And hence, each potential child is a huge cost.